Change inspired by PEP 0290 (Code Migration and Modernization):

Since there is only one None object, equality can be tested with identity. Identity tests are slightly faster than equality tests. Also, some object types may overload comparison, so equality testing may be much slower.

Pattern::

if v == None  -->  if v is None:
if v != None  -->  if v is not None:

The existing code runs without errors, there is no need to fix this other than "modernization" of the code.